Kingdom Hearts is a very popular series, so there are many cosplayers of pretty much each character. Nevertheless, how often they are cosplayed shouldn't effect your choice. If you want to be a character, be it. (and strive to be the best one you can, so you can stand out among the others! lol)

I agree that it is area based. In my area I've noticed a decline, the largest amount is at the biggest cons. It's usually Organization (Axel, Demyx, Xexion) members or a group of the main three characters.

If you're concerned able their being too many of your first choice you could always do a less done version. It might require more work/effort but it could also make it stand out more.

Like others said, it depends on the area and convention... larger cons like Otakon and AX are going to have the largest number of KH cosplayers. It's going to be even more because of the 3DS game coming out soon.

If you're worried about doing an overdone costume, maybe try an alternate outfit? I know Riku gets at least one new costume for Dream Drop Distance, you could try one of those.

if you think the character might be overdone, but you still want to do it anyway, you could maybe try doing something that will make YOUR version of the costume unique? I also cosplay KH2 and 358/2days Riku. But when I do OrgXIII, I use an Oblivion (or carry a plush heartless depending on whether my keyblade's been banned from con)...and my normal KH2 Riku I have a way to dawn that's taller than my Roxas. >.>

Finding ways to make yourself different from the other people in the same costume is one of the fun parts of cosplay?

Like others said, it depends on the area and convention... larger cons like Otakon and AX are going to have the largest number of KH cosplayers. It's going to be even more because of the 3DS game coming out soon.

If you're worried about doing an overdone costume, maybe try an alternate outfit? I know Riku gets at least one new costume for Dream Drop Distance, you could try one of those.

Agreed. Less people have done the DDD versions. I didn't see any of these at Otakon or Zenkaikon not counting myself.

But do what you want, and do a good job. People will still like it! I personally don't mind seeing people cosplay the same outfits all over the place. c:

The more it's done, the harder it is to get recognition. But it also makes it easier to find tutorials/parts/materials. And also you have more people to interact with. :3 So long as you're not into the competition part of cosplay. If you are, then you can have even more motivation to make yours one of the best.